Thermopile differential thermal analysis sensor

Abstract

A differential thermal analysis sensor consisting of two low-impedance differential thermopiles. Each thermopile consists of a series of thermocouples joined in series, with the measuring junctions of the thermocouples arranged around a uniform temperature measuring region, and the thermoelectric reference junctions of the thermocouples arranged around a uniform temperature thermoelectric reference region. The differential thermal analysis sensor can be used for single-sample heat flux differential thermal analysis measurements, dual-sample heat flux differential thermal analysis measurements, or power compensation differential thermal analysis measurements.

What is claimed is: 
     
       1. A differential thermal analysis sensor comprising: (a) a substrate having a surface;   (b) a first thermopile attached to said surface of said substrate, said first thermopile having a first set of measuring junctions positioned around a first measuring zone, and a first set of thermoelectric reference junctions, wherein said first set of thermoelectric reference junctions are attached to the substrate, said first thermopile being characterized by a low electrical impedance;   (c) a second thermopile attached to said surface of said substrate, said second thermopile having a second set of measuring junctions positioned around a second measuring zone, and a second set of thermoelectric reference junctions, said second thermopile also being characterized by a low electrical impedance; and   (d) a first layer of insulating material electrically insulating said first thermopile from said second thermopile, wherein said second set of thermoelectric reference junctions are attached to said first layer of insulating material, and wherein   the thermoelectric reference junctions of said first thermopile and the thermoelectric reference junctions of said second thermopile are positioned in a common reference zone.   
     
     
       2. The differential thermal analysis sensor of claim 1, wherein the first and second thermopiles are each comprised of in-series thermocouples, said thermocouples being comprised of thermoelements fabricated using thin film techniques. 
     
     
       3. The differential thermal analysis sensor of claim 1, wherein the first and second thermopiles are each comprised of in-series thermocouples, said thermocouples being comprised of thermoelements fabricated using thick film techniques. 
     
     
       4. The differential thermal analysis sensor of claim 1, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       5. The differential thermal analysis sensor of claim 1, wherein the measuring junctions of the first and second thermopiles are equally spaced in a circular pattern around the first and second measuring zones, respectively. 
     
     
       6. The differential thermal analysis sensor of claim 1, wherein the common reference zone is a circular region surrounding the measuring junctions, and the thermoelectric reference junctions are arranged in a circular pattern in the common reference zone. 
     
     
       7. The differential thermal analysis sensor of claim 1, wherein the substrate is circular. 
     
     
       8. The differential thermal analysis sensor of claim 7, wherein the centers of the first and second measuring zones are symmetrically positioned on a diameter of the circular substrate on either side of the center of the circular substrate. 
     
     
       9. The differential thermal analysis sensor of claim 1, further comprising a first thermocouple for measuring the temperature of the first measuring zone, and a second thermocouple for measuring the temperature of the second measuring zone. 
     
     
       10. The differential thermal sensor of claim 1, wherein the substrate has a low thermal diffusivity, such that the sensor is characterized by having very high calorimetric sensitivity. 
     
     
       11. The differential thermal analysis sensor of claim 1, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       12. A heat flux differential scanning calorimetry method comprising: (a) providing a differential temperature sensor in an enclosure, said differential temperature sensor comprising two low electrical impedance thermopiles applied to a single substrate, each thermopile having a set of measuring junctions and a set of thermoelectric reference junctions, the measuring junctions of each thermopile being positioned in its own separate measuring zone, and the thermoelectric reference junctions of the two thermopiles being attached to the substrate in a reference zone common to the two thermopiles;   (b) placing a reference material on one measuring zone and a sample on the other measuring zone;   (c) controlling the temperature of the enclosure according to a predetermined heating rate program;   (d) combining the output of the two thermopiles; and   (e) recording the difference in the temperature of the sample material and the reference material as a function of the temperature of the sample.   
     
     
       13. The heat flux differential scanning calorimetry method of claim 12, further comprising: (f) plotting the difference in the temperature of the sample material and the reference material as a function of the temperature of the sample;   (g) identifying at least one transition;   (h) determining the baseline for at least one of the transitions identified in step (g); and   (i) determining the total heat of transition of the at least one transition.   
     
     
       14. The heat flux differential scanning calorimetry method of claim 12, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       15. The heat flux differential scanning calorimetry method of claim 12, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       16. The heat flux differential scanning calorimetry method of claim 12, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       17. A dual-sample heat flux differential scanning calorimetry method comprising: (a) providing a differential temperature sensor in an enclosure, said differential temperature sensor comprising two low electrical impedance measuring thermopiles applied to a single substrate, each thermopile having a set of measuring junctions and a set of thermoelectric reference junctions, the measuring junctions of each thermopile being positioned in its own separate measuring zone, and the thermoelectric reference junctions of the two thermopiles being attached to the substrate in a reference zone common to the two thermopiles;   (b) placing a reference material on each measuring zone;   (c) controlling the temperature of the enclosure according to a predetermined heating rate program;   (d) recording the output of the two thermopiles;   (e) placing a sample material on each measuring zone;   (f) controlling the temperature of the enclosure according to the predetermined heating rate program;   (g) recording the output of the two thermopiles;   (h) separating the signals of the two reference materials;   (i) separating the signals of the two sample materials; and   (j) combining the results of each sample material measurement with the results of its respective reference material measurement to obtain heat flux data for each sample with respect to its respective reference material,   wherein step (H) may be performed any time after step (d) and before step (j), and step (i) may be performed any time after step (g) and before step (j).   
     
     
       18. The heat flux differential scanning calorimetry method of claim 17, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       19. The heat flux differential scanning calorimetry method of claim 17, further comprising: (k) plotting the heat flux data as a function of the temperature of the sample material to obtain a plot of the heat flux as a function of temperature for each sample material;   (l) identifying at least one transition in each plot;   (m) determining the baseline for at least one of the transitions identified in-step (k); and   (n) determining the total heat of transition of the at least one transition.   
     
     
       20. The heat flux differential scanning calorimetry method of claim 17, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       21. The heat flux differential scanning calorimetry method of claim 17, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       22. A power compensated differential scanning calorimetry method comprising: (a) providing a differential temperature sensor in an enclosure, said differential temperature sensor comprising two thermopiles applied to a single substrate such that each thermopile has an independent temperature controlled zone, and a heat source/sink zone which is common to both thermopiles, said differential temperature sensor including thermocouples for measuring the temperature of each of the temperature controlled zones, each thermopile having a set of temperature-controlling junctions and a set of heat source/sink junctions, the temperature-controlling junctions of each thermopile being positioned in its own separate temperature-controlling zone, and the heat source/sink junctions of the two thermopiles being attached to the substrate in a heat source/sink zone common to the two thermopiles;   (b) placing a sample material on one of the temperature controlled zones and a reference material on the other temperature controlled zone;   (c) controlling the temperature of the enclosure according to a predetermined heating rate program;   (d) independently supplying direct current electrical currents to each of the thermopiles such that the thermopiles pump heat to and from the heat source/sink regions to the temperature controlled region such that the temperature difference between the sample and reference materials is suppressed; and   (e) measuring and recording the direct current electrical currents supplied to each of the thermopiles.   
     
     
       23. The power compensated differential scanning calorimetry method of claim 22, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       24. The power compensated differential scanning calorimetry method of claim 22, further comprising: (f) calculating the heat flow to the sample material;   (g) calculating the heat flow to the reference material;   (h) plotting the difference between the heat flow to the sample material and the heat flow to the reference material as a function of the temperature of the sample to obtain a heat flow plot;   (i) identifying at least one transition in the heat flow plot;   (h) determining the baseline for at least one of the transitions identified in step (i); and   (j) determining the total heat of transition of the at least one transition.   
     
     
       25. The power compensated differential scanning calorimetry method of claim 22, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       26. The power compensated differential scanning calorimetry method of claim 22, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       27. A dual sample power compensated differential scanning calorimetry method comprising: (a) providing a differential temperature sensor in an enclosure, said differential temperature sensor comprising a first and a second thermopile applied to a single substrate such that the first thermopile has a first independent temperature controlled zone and the second thermopile has a second independent temperature controlled zone, and a heat source/sink zone which is common to both thermopiles, said differential temperature sensor including a first thermocouple for measuring the temperature of the first temperature controlled zone and a second thermocouple for measuring the temperature of the second temperature controlled zone, each thermopile having a set of temperature-controlling junctions and a set of heat source/sink junctions, the temperature-controlling junctions of each thermopile being positioned in its own separate temperature-controlling zone, and the heat source/sink junctions of the two thermopiles being attached to the substrate in a heat source/sink zone common to the two thermopiles;   (b) placing a first reference material on the first temperature controlled zone and a second reference material on the second temperature controlled zone;   (c) controlling the temperature of the enclosure according to a predetermined heating rate program;   (d) independently supplying direct current electrical currents to the first thermopile and to the second thermopile such that the first and second thermopiles pump heat to and from the heat source/sink regions to the temperature controlled region such that the temperature difference measured by the first thermocouple and the second thermocouple is suppressed;   (e) measuring and recording the direct current electrical current supplied to the first thermopile and the direct current electrical current supplied to the second thermopile   (f) placing a first sample material on the first temperature controlled zone and a second sample material on the second temperature controlled zone;   (g) controlling the temperature of the enclosure according to the predetermined heating rate program;   (h) independently supplying direct current electrical currents to the first thermopile and to the second thermopile such that the first and second thermopiles pump heat to and from the heat source/sink regions to the temperature controlled region such that the temperature difference measured by the first thermocouple and the second thermocouple is suppressed;   (i) measuring and recording the direct current electrical current supplied to the first thermopile and the direct current electrical current supplied to the second thermopile;   (j) combining the results of the sample material measurement with the results of the first reference material measurement to obtain heat flux data for the first sample with respect to the first reference material; and   (k) combining the results of the second sample material measurement with the results of the second reference material measurement to obtain heat flux data for the second sample with respect to the second reference material,   wherein steps (b)-(e) may be performed either before or after steps (f)-(i), step (j) may be performed at any point after step (e), and step (k) may be performed at any point after step (i).   
     
     
       28. The dual sample power compensated differential scanning calorimetry method of claim 27, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       29. The dual sample power compensated differential scanning calorimetry method of claim 27, further comprising: (l) calculating the heat flow to the sample materials;   (m) calculating the heat flow to the reference materials;   (n) plotting the difference between the heat flow to the sample materials and the heat flow to their respective reference materials as a function of the temperature of the samples;   (o) identifying at least one transition in each plot so obtained;   (p) determining the baseline for at least one of the transitions identified in step (o); and   (q) determining the total heat of transition of the at least one transition.   
     
     
       30. The dual sample power compensated differential scanning calorimetry method of claim 27, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       31. The dual power compensated differential scanning calorimetry method of claim 27, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       32. The differential thermal analysis sensor of claim 1, further comprising (e) a second layer of insulating material attached to said substrate over said second thermopile;   (f) a third thermopile attached over said second layer of insulating material to said surface of said substrate, said third thermopile having a third set of measuring junctions positioned around a third measuring zone, and a third set of thermoelectric reference junctions, wherein said third set of thermoelectric reference junctions are attached to the second layer of insulating material, said third thermopile also being characterized by a low electrical impedance;   (g) a third layer of insulating material attached to said substrate over said third thermopile; and   (h) a fourth thermopile attached over said third layer of insulating material to said major surface of said substrate, said fourth thermopile having a fourth set of measuring junctions positioned around a fourth measuring zone, and a fourth set of thermoelectric reference junctions, wherein said thermoelectric reference junctions are attached to the third layer of insulating material, said fourth thermopile also being characterized by a low electrical impedance;   wherein said first, second, third and fourth thermopiles have a common reference zone.   
     
     
       33. The differential thermal analysis sensor of claim 22, wherein the substrate is a high thermal diffusivity material, such that the sensor is characterized by having a high resolution. 
     
     
       34. The differential thermal analysis sensor of claim 32, wherein the first, second, third and fourth thermopiles are each comprised of in-series thermocouples, said thermocouples being comprised of thermoelements fabricated using thin film techniques. 
     
     
       35. The differential thermal analysis sensor of claim 32, wherein the first, second, third and fourth thermopiles are each comprised of in-series thermocouples, said thermocouples being comprised of thermoelements fabricated using thick film techniques. 
     
     
       36. The differential thermal analysis sensor of claim 32, wherein the first, second, third and fourth thermopiles are each comprised of in-series thermocouples having measuring junctions and thermoelectric reference junctions, the measuring junctions of said thermocouples of each said thermopile being arranged in a circular pattern to form each measuring zone. 
     
     
       37. The differential thermal sensor of claim 32, wherein the substrate has a low thermal diffusivity, such that the sensor is characterized by having very high calorimetric sensitivity. 
     
     
       38. The differential thermal analysis sensor of claim 32, wherein the substrate has a moderate thermal diffusivity, such that the sensor is characterized by having high calorimetric sensitivity. 
     
     
       39. The differential scanning calorimeter comprising: (a) a temperature-controlled enclosure;   (b) a differential thermal sensor placed within the enclosure having a first low-impedance thermopile and a second low-impedance thermopile, wherein the first low-impedance thermopile comprises a first set of measuring junctions positioned around a first measuring position and the second low-impedance thermopile comprises a second set of measuring junctions positioned around a second measuring position, wherein each thermopile also comprises a set of thermoelectric reference junctions, and wherein the thermoelectric reference junctions of the first and second thermopiles are positioned in a common reference zone, said thermoelectric reference junctions being attached to the substrate such that the reference junctions of the first and second thermopiles are coincident;   (c) a first differential temperature amplifier and a second differential temperature amplifier, electrically connected to the differential thermal sensor such that the output of the first thermopile is fed to the first differential temperature amplifier and the output of the second thermopile is fed to the second differential temperature amplifier;   (d) analog to digital converters connected to each of the differential temperature amplifiers for converting the outputs of the temperature amplifiers into digital data; and   (e) means for combining and storing the digital data, and means for calculating the heat flow to and from the first position relative to the heat flow to and from the second position.   
     
     
       40. The differential scanning calorimeter of claim 39, further comprising means for providing thermal programs to control the temperature of the enclosure according to the thermal programs, and means for analyzing the heat flow data. 
     
     
       41. The differential scanning calorimeter of claim 39, further comprising a first thermocouple for measuring the temperature of the first position, a second thermocouple for measuring the temperature of the second position, and means for feeding the output of said first and second thermocouple to said means for combining and storing the digital data. 
     
     
       42. A power compensation differential scanning calorimeter comprising: (a) a temperature-controlled enclosure;   (b) a differential thermal sensor placed within the enclosure having a first low-impedance thermopile and a second low-impedance thermopile, wherein the first low-impedance thermopile pumps heat to and from a temperature-controlling junction at a first position from and to a first heat source/sink junction and the second low-impedance thermopile pumps heat to and from a temperature-controlling junction at a second position from and to a second heat source/sink junction, the temperature-controlling junctions of each thermopile being positioned in its own separate temperature-controlling zone, and the heat source/sink junctions of the two thermopiles being attached to the substrate in a heat source/sink zone common to the two thermopiles, and wherein the heat source/sink junctions of the first and second thermopiles are coincident;   (c) a first thermocouple measuring the temperature of the first position and a second thermocouple measuring the temperature of the second position;   (d) means for controlling the current to the first and second thermopiles so as to suppress the difference in the temperatures measured by the first and second thermocouples;   (e) means for recording the currents supplied to the first and second thermocouples as a function of the temperature measured by the first thermocouple; and   (f) means for calculating the heat flow to and from the first position relative to the heat flow to and from the second position, as a function of the temperature measured by the first thermocouple, from the difference between the current supplied to the first thermopile and the current supplied to the second thermopile.   
     
     
       43. The power compensation differential scanning calorimeter of claim 43, further comprising means for switching the calorimeter from single-sample operation to dual sample operation.